Hereinafter, a carrier will be briefly described.
A user may perform a modulation operation with respect to the amplitude, frequency and/or phase of a sine wave and a periodic pulse wave. A sine wave or a pulse wave for carrying information is called a carrier.
Examples of a carrier modulation scheme include a Single-Carrier Modulation (SCM) scheme and a Multicarrier Modulation (MCM) scheme. Among others, the SCM scheme is to perform modulation with respect to all information carried on one carrier.
The MCM scheme refers to a technology of dividing an overall bandwidth channel of one carrier into several sub-channels each having a small bandwidth and transmitting a plurality of narrowband sub-carriers through the sub-channels.
In the MCM scheme, each of the sub-channels is approximated so as to have a flat channel due to the small bandwidth. A user can compensate for distortion of a channel using a simple equalizer. In addition, the MCM scheme is implemented at a high speed using Fast Fourier Transform (FFT) and is more advantageous in high-speed data transmission than the SCM scheme.
As capability of a base station and/or a terminal have been developed, a frequency bandwidth provided or used by the base station and/or the terminal has expanded and throughput of data processed by the terminal has been increased. Accordingly, in the embodiments of the present invention, a multicarrier system supporting a wideband by aggregating one or more carriers is disclosed, unlike the above-described MOM scheme.
For example, in order to increase transmit capacity of radio data, a bandwidth of 200 KHz to 1.25 MHz has been used in second-generation radio communication and a bandwidth of 5 MHz to 10 MHz has been used in third-generation radio communication. A bandwidth is increased to 20 MHz in a 3GPP LTE system or an IEEE 802.16m system as a fourth-generation wireless access system which has been currently developed.
A method of increasing a bandwidth in order to increase transmit capacity of radio data is inevitable. However, in this case, since a large bandwidth is supported even when the level of a desired service is low, power consumption is very high. In addition, a current system may not be reused in order to support such requirements.
In order to solve such problems, a multicarrier transmission method of simultaneously transmitting and receiving data using several bandwidths has been researched. A multicarrier system may use multiple carriers which are contiguously located on a frequency axis or multiple carriers which are separated on a frequency axis.